U.S. patent number 7,385,751 [Application Number 11/292,802] was granted by the patent office on 2008-06-10 for process for imagewise opening and filling color display components and color displays manufactured thereof.
This patent grant is currently assigned to SiPix Imaging, Inc.. Invention is credited to Xianhai Chen, Rong-Chang Liang, Zarng-Arh George Wu, HongMei Zang.
United States Patent |
7,385,751 |
Chen , et al. |
June 10, 2008 |
Process for imagewise opening and filling color display components
and color displays manufactured thereof
Abstract
This invention relates to the field of electrophoretic displays.
In particular, it relates to imagewise opening, filling and sealing
multicolor display components and the manufacture of multicolor
displays.
Inventors: |
Chen; Xianhai (San Jose,
CA), Zang; HongMei (Sunnyvale, CA), Wu; Zarng-Arh
George (Sunnyvale, CA), Liang; Rong-Chang (Cupertino,
CA) |
Assignee: |
SiPix Imaging, Inc. (Fremont,
CA)
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Family
ID: |
46205795 |
Appl.
No.: |
11/292,802 |
Filed: |
December 2, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060132897 A1 |
Jun 22, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10284586 |
Oct 30, 2002 |
6972893 |
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09879408 |
Jun 11, 2001 |
6545797 |
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Current U.S.
Class: |
359/296; 430/38;
430/34; 430/32 |
Current CPC
Class: |
G02F
1/133377 (20130101); G02F 1/1679 (20190101); G02F
1/1341 (20130101); G02F 1/167 (20130101); G02F
1/1347 (20130101); G02F 1/1681 (20190101) |
Current International
Class: |
G02B
26/00 (20060101) |
Field of
Search: |
;359/296 ;245/105,107
;430/323,438,32,34,38 ;204/450,600 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1 313 412 |
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Apr 1973 |
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GB |
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WO 01/67170 |
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Sep 2001 |
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WO |
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WO 02/01280 |
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Jan 2002 |
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WO |
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WO 02/01281 |
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Jan 2002 |
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WO |
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WO 02/056097 |
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Jul 2002 |
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WO |
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WO 02/065215 |
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Aug 2002 |
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WO |
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WO 03/081325 |
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Oct 2003 |
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WO |
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Primary Examiner: Sugarman; Scott J.
Assistant Examiner: Tra; Tuyen
Attorney, Agent or Firm: Howrey LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. application Ser.
No. 10/284,586 filed Oct. 30, 2002, now U.S. Pat. No. 6,972,893;
which is a continuation-in-part of U.S. application Ser. No.
09/879,408, filed Jun. 11, 2001, now U.S. Pat. No. 6,545,797; the
contents of all of which are incorporated herein by reference in
their entirety.
Claims
What is claimed is:
1. A process for the manufacture of a multicolor display, which
process comprises: (a) filling all display cells with a filler
material; (b) removing the filler material from selected display
cells; (c) filling said selected display cells with a display fluid
of a first color; (d) sealing said selected display cells that are
filled with said display fluid of the first color; and (e)
repeating steps (b) through (d) to fill and seal display fluids of
different colors in display cells which are still filled with the
filler material.
2. The process of claim 1 wherein said filler material is selected
from the group consisting of organic, inorganic and polymer
particulates, water soluble and dispersible polymers and mixtures
thereof.
3. The process of claim 1 wherein said filler material is selected
from the group consisting of water-dispersible branched
sulfopolyesters, carboxylated acrylic-based polymers, poly(vinyl
alcohol), polyvinylpyrrolidone, poly(4-vinyl phenol), pre-exposed
positive photoresists, polyacrylic acid, polymethacrylic acid, and
their copolymers, zinc ionomer of ethylene copolymer, sodium
ionomer dispersion of ethylene acrylic acid copolymer, and
N,N-diethylethanolamine dispersions, non-film forming latexes,
colloidal silica, and mixtures thereof.
4. The process of claim 3 wherein said non-film forming latex is
PMMA or polystyrene latex.
5. The process of claim 1 wherein step (b) is carried out by
coating said display cells filled with said filler material with a
layer of photoresist, followed by imagewise exposing and developing
the photoresist to selectively open the display cells filled with
said filler material and remove the filler material.
6. The process of claim 5 wherein said layer of photoresist has a
thickness in the range of about 0.5 to 15 microns.
7. The process of claim 6 wherein said layer of photoresist has a
thickness in the range of about 1 to 3 microns.
8. The process of claim 5 wherein said photoresist is a
novolac-based photoresist.
9. The process of claim 5 wherein said photoresist is a
polyvinylphenol-based photoresist.
10. The process of claim 5 wherein said photoresist is a t-BOC
derivative of polyvinylphenol-based photoresist.
11. The process of claim 5 wherein said exposing step is performed
by UV radiation, visible light or other radiation sources.
12. The process of claim 11 further comprising the step of soft
baking the photoresist before said exposing step.
13. The process of claim 5 wherein said developing step comprises
contacting exposed display cells with a developing solution.
14. The process of claim 13 wherein said developing solution is a
base developer selected from the group consisting of alkaline
solutions, sodium hydroxide, sodium tetraborate decahydrate and
borate solution and potassium hydroxide and borate solution.
15. The process of claim 13 wherein said developing solution
comprises an additive.
16. The process of claim 15 wherein said additive is a surfactant
or dispersing agent.
17. The process of claim 5 further comprising the step of washing
the developed display cells with a solvent or a mixture of
solvents.
18. The process of claim 17 wherein said solvent is distilled water
or deionized water.
19. The process of claim 1 wherein said filler material is capable
of being readily removed from the display cells by using a cleaning
solution which is a weak solvent or non-solvent for the non-exposed
photoresist, but is a good solvent or dispersion medium for the
filler material.
20. The process of claim 19 wherein said cleaning solution is an
aqueous solution.
21. The process of claim 1 wherein said filler material comprises
an additive selected from the group consisting of surfactants,
dispersing agents and photosensitive dissolution-inhibiting
compounds.
22. The process of claim 21 wherein said photosensitive
dissolution-inhibiting compound is a diazide compound.
23. The process of claim 1 wherein said filler material is a
pre-exposed positive working novolac photoresist.
24. The process of claim 1 wherein said display fluid is an
electrophoretic fluid comprising charged pigment particles
dispersed in a dielectric solvent.
25. The process of claim 24 wherein said pigment particles are
white particles.
26. The process of claim 1 wherein said display fluid comprises
liquid crystals.
27. The process of claim 26 wherein said liquid crystals comprise a
dichroic dye.
28. The process of claim 1 wherein said sealing step is carried out
with a sealing composition which has a specific gravity lower than
that of said display fluid.
29. The process of claim 28 wherein said sealing step is carried
out by overcoating said sealing composition on said display
fluid.
30. The process of claim 28 wherein said sealing step is carried
out by filling said display fluid with said sealing composition
dispersed therein.
31. The process of claim 1 which is carried out continuously or
semi-continuously.
32. The process of claim 1 wherein step (c) is carried out by
screen printing, gravure printing or inkjet printing.
Description
FIELD OF INVENTION
This invention relates to the field of electrophoretic displays. In
particular, it relates to imagewise opening and filling multicolor
display components and the manufacture of multicolor displays.
BACKGROUND OF THE INVENTION
Electrophoretic displays (EPDs) are known non-emissive displays
suitable for use in the display of digital, alphanumeric, analog or
graphical information. An EPD system typically comprises a
suspension of pigment particles in a dielectric liquid held between
two electrodes, at least one of which is transparent. Applied
potential across the electrodes causes the charged particles to
migrate to one or the other electrode. Where the suspension
includes pigment particles and a dielectric liquid of contrasting
colors, the movement of the pigment particles will cause images to
be displayed, which are visible through the transparent
electrode(s) or a viewing sheet.
EPDs have attributes of excellent brightness and contrast, wide
view angles, bistability and low power consumption when compared
with liquid crystal displays. The basic technology associated with
the development and manufacture of EPD's has been disclosed in U.S.
Pat. Nos. 5,961,804, 4,732,830, 4,680,103, 4,298,448, 4,732,830 and
cited patents therein; and the disclosures of these patents are
incorporated herein by reference in their entirety.
Among the advantages of an EPD over other types of flat panel
displays is the very low power consumption. This salient advantage
makes the EPD particularly suitable for portable and battery
powered devices such as laptops, cell phones, personal digital
assistants, portable electronic medical and diagnostic devices,
global positioning system devices and the like.
In order to prevent undesired movements of particles such as
sedimentation in the dielectric fluid, partitions were proposed
between the two electrodes for dividing the space into smaller
cells. See for example, M. A Hopper and V. Novotny, IEEE Trans.
Electr. Dev., Vol ED 26, No. 8, pp. 1148-1152 (1979). However, the
filling and sealing processes of electrophoretic fluids in these
cells are of very low throughput and high cost.
Attempts have been made to enclose the suspension in microcapsules.
U.S. Pat. Nos. 5,961,804 and 5,930,026 describe microencapsulated
EPDs. These displays have a substantially two dimensional
arrangement of microcapsules each having therein an electrophoretic
composition of charged pigment particles suspended in a dielectric
fluid that visually contrasts with the particles.
U.S. Pat. Nos. 6,930,818 and 6,933,098 (the '818 and '098 Patents),
assigned to the same inventive entity, describe EPDs comprising
microcups of well-defined shape, size and aspect ratio, filled with
charged pigment particles dispersed in an optically contrasting
dielectric solvent. The methods of manufacturing such microcups
have also been described in the '818 and '098 Patents and are
incorporated by reference herein in their entirety.
The methods of preparing the improved color EPD disclosed in the
'818 and '098 Patents include laminating preformed empty microcups
with a layer of positively working photoresist, imagewise exposure
of the positive photoresist to selectively open a certain number of
microcups, developing the photoresist, filling the selectively
opened microcups with a colored electrophoretic fluid, and sealing
the filled microcups. The sequence of opening and developing the
photoresist, and filling and sealing of the microcups may be
performed in iterative steps to create sealed microcups filled with
electrophoretic fluids of different colors.
One aspect of the above cited '818 Patent relates to a novel
roll-to-roll process and apparatus which permit the manufacture of
a display to be carried out continuously by a synchronized
photolithographic process. The synchronized roll-to-roll process
and apparatus are also useful for manufacturing liquid crystal
displays (LCD) and other structures and assemblies for electronic
devices.
The '098 Patent also describes the manufacture of a plurality of
microcups which are formed integrally with one another as portions
of a structured two-dimensional array assembly, being formed upon a
support web including a patterned conductor film, such as
addressable indium-tin oxide (ITO) lines. Each microcup of the
array assembly is filled with a suspension or dispersion of charged
pigment particles in a dielectric solvent, and sealed to form an
electrophoretic cell.
The substrate web upon which the microcups are formed includes a
display addressing array comprising pre-formed conductor film, such
as ITO conductor lines. The conductor film (ITO lines) and support
web are coated with a radiation curable layer. The film and
radiation curable layer are then exposed imagewise to radiation to
form the microcup wall structure. Following exposure, the unexposed
area is removed by using a developer, leaving the cured microcup
walls bonded to the conductor film/support web. The imagewise
exposure may be by UV or other forms of radiation through a
photomask to produce an image or predetermined pattern of exposure
of the radiation curable material coated on the conductor film.
Although it is generally not required for most applications, the
mask may be positioned and aligned with respect to the conductor
film, i.e., ITO lines, so that the transparent mask portions align
with the spaces between ITO lines, and the opaque mask portions
align with the ITO material. The '818 and '098 Patents also
describe a microcup array prepared by a process including embossing
a thermoplastic or thermoset precursor layer coated on a conductor
film with a pre-patterned male mold, followed by releasing the
mold. The precursor layer may be hardened by radiation, cooling,
solvent evaporation, or other means. Solvent-resistant and
thermomechanically stable microcups having a wide range of size,
shape, pattern, and opening ratio can be prepared by either one of
the aforesaid methods.
In addition, the above cited '818 and '098 Patents describe the
manufacture of a monochrome EPD from a microcup assembly by filling
the microcups with a single pigment suspension composition, sealing
the microcups, and finally laminating the sealed array of microcups
with a second conductor film pre-coated with an adhesive layer.
The '818 and '098 Patents also relate to the manufacture of a color
EPD from a microcup assembly by a process of sequential selective
opening and filling of predetermined microcup subsets. The process
includes laminating or coating the pre-formed microcups with a
layer of positively working photoresist, selectively opening a
certain number of the microcups by imagewise exposing the positive
photoresist, followed by developing the photoresist, filling the
opened microcups with a colored electrophoretic fluid, and sealing
the filled microcups by a sealing process. These steps may be
repeated to create sealed microcups filled with electrophoretic
fluids of different colors for a color EPD.
The '098 Patent also describes a synchronized roll-to-roll
photolithographic exposure method and apparatus, which may be
employed for a number of useful processes, including the process of
making the microcup array and the process of selectively filling of
the array of microcups to form a color display assembly. The
imagewise roll-to-roll photolithographic exposure is performed
through a moving photomask synchronized with a moving web
substrate, to permit imagewise exposure of the workpiece (e.g.,
microcup array or color display) in a continuous or semi-continuous
and seamless manner. This synchronized roll-to-roll exposure
photolithographic process is also amenable for the manufacture of
color displays.
The synchronized roll-to-roll process may be adapted to the
preparation of a wide range of structures or discrete patterns for
electronic devices formable upon a support web substrate, e.g.,
patterned ITO films, flexible circuit boards or the like.
However, where the manufacture of high contrast ratio color
displays requires the use of microcups that are structurally wide
and deep, resulting in relatively thin partitions between the
microcups, defects in the finished displays are often observed.
These defects may be attributed to, in part, defects in various
individual manufacturing steps, including poor mechanical and
dissolution characteristics of the positive photoresist, error in
the undercutting of the photoresist by a developer, and poor
adhesion of the photoresist to the walls or partitions of the
microcups. These manufacturing defects appear as indefinite
microcup structures and adversely affect the quality of the display
images. Therefore, there exists a need for a defect free
manufacturing process for imagewise opening the microcups and
filling them with selectively colored electrophoretic fluid for
color EPDs.
SUMMARY OF THE INVENTION
In the broadest application of this invention, the innovative
approach for the manufacture of multicolor displays involves the
sequence of filling the microcups array with a removable temporary
filler material which can be removed or washed away later by a
developer used for the positively working photoresist, coating onto
the filled microcups a positively working photoresist, imagewise
exposing and developing the photoresist, removing the filler
material during or after the photoresist development process,
filling the emptied microcups with colored display fluids, and
finally sealing the filled microcups by a sealing process disclosed
in the co-pending '818 and '098 Patents. The same iterative process
is then performed with different colored display fluids for
multicolor displays.
The steps of adding and removing the temporary fillers serve to
maintain structural integrity of the photoresist layer coated on
the microcups in the non-imaging area, particularly for the
photoresist coated on microcups having large and deep openings such
as 50 to 200 microns in diameter and a depth in the range of 3 to
100 microns, preferably about 5 to 50 microns. The steps also
eliminate the need of a tenting adhesive layer between the
photoresist and the microcup array. The manufacturing process of
this invention provides a much wider process and material latitude
in the manufacture of high definition multicolor displays.
Various color display media or suspensions of different colors,
compositions, liquid crystals, or any other suitable display fluids
for generating multicolor displays known in the art may be
used.
The resulting simple and efficient manufacturing processes
disclosed in this application provide high quality, high resolution
multi-color displays with significantly lower processing costs,
less defects, higher yields, and no crosstalk among neighboring
color fluids. These multi-step processes may also be carried out
efficiently under roll-to-roll manipulation or processing as known
in the art, or they may be carried out in batch operations, or
conveyed through continuous or semi-continuous operations.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1A-1H illustrate various features of the invention of the
process for the imagewise opening and filling of multi-color
display components and the manufacture of the display.
FIG. 1A illustrates the microcups formed from various compositions
of thermoplastic or thermoset precursor (1) on a conductor film (2)
and substrate (3).
FIG. 1B illustrates the microcup array filled with a removable
filler material (4) with a coating comprising a layer of positive
photoresist (5).
FIG. 1C illustrates the result of the first imagewise exposure of
the positive photoresist by radiation, development and removal of
the coating, and removal of the filler material, producing the
developed and cleaned microcups.
FIG. 1D illustrates the result of the first filling and sealing of
the opened microcups with a first color display fluid (6).
FIG. 1E illustrates the result of the second imagewise exposure of
the positive photoresist by radiation, development and removal of
the coating, and the removal of the filler material, producing the
developed and cleaned microcups.
FIG. 1F illustrates the result of the second filling and sealing of
the opened microcups with a second color display fluid (7).
FIG. 1G illustrates the third imagewise exposure of the positive
photoresist by radiation, development and removal of the coating,
and the removal of the filler material, producing the developed and
cleaned microcups.
FIG. 1H illustrates the result of the third filling and sealing of
the opened microcups with a third color display fluid (8).
DETAILED DESCRIPTION OF THE INVENTION
In the first aspect of this invention, microcups formed on a
conductor substrate such as ITO/PET film, are filled with a
removable temporary filler material. Microcups used for this
invention may be circular, symmetrical or asymmetrical polygonal
shapes with an opening area ranging from about 4 microns.sup.2 to
about 5.times.10.sup.5 microns.sup.2, preferably from about
10.sup.3 microns.sup.2 to about 5.times.10.sup.4 microns.sup.2. The
depth may be in the range of about 5 to about 100 microns,
preferably from about 10 to about 50 microns. The depth to width
ratio may be in the range of about 0.01 to 5, preferably from about
0.1 to 2.5.
The microcups may be arranged in many different geometric and
non-geometric patterns, such as circles, polygonal such as squares,
rectangular, diamond, triangular or combination thereof, for
example, or they may be arranged in 2 or 3 dimensional, symmetrical
or asymmetrical distributions such as a plurality of rows, columns
or various combinations thereof to optimize the desired visual
image of the displays.
The microcups may be prepared from various compositions of
thermoplastic or thermoset precursor as described in co-pending
'818 and '098 Patents assigned to the same inventive entity. The
precursors may comprise multifunctional or polyvalent acrylates or
methacrylates, cyanoacrylates, polyvalent vinyls including
divinylbenzene, divinylsilane, polyvalent vinylethers, polyvalent
epoxides, polyvalent allyls, and oligomers or polymers containing
the above-mentioned crosslinkable functional groups or the like.
Most preferably, the thermoplastic or thermoset precursor
composition comprises multifunctional acrylates and their
oligomers. A crosslinkable oligomer imparting flexibility, such as
urethane acrylates, polybutadiene (and its copolymers), diacrylate,
or polyester acrylates, is usually added to improve the flexure
resistance of the embossed microcups. The composition of the
microcups may contain oligomers, monomers, additives and optionally
a polymer. More than one crosslinking mechanism may be employed.
Examples include the use of hybrid of radical and cationic or ring
opening polymerization mechanisms.
The '818 Patent describes EPDs comprising microcups of well-defined
shape, size, pattern, and aspect ratio, and the microcups are
filled with charged pigment particles dispersed in an optically
contrasting dielectric solvent. In addition, their methods of
manufacture have also been described in the same patent and are
incorporated by reference herein in their entirety.
In the present invention, the microcup array was first filled with
a removable temporary filler material, and then coated with a layer
of positive photoresist. Suitable fillers for application in this
invention, include materials which do not react with or adversely
affect the integrity of the microcups or the unexposed photoresist
and can be readily removed during or after the development of the
photoresist.
Suitable fillers used in the present invention may include
materials that may be readily removed or washed out of the
microcups using a cleaning solution such as acidic or basic
solutions (such as developers for positive photoresist), aqueous or
non-aqueous solvents or solvent mixtures that do not adversely
affect or react with the microcups or the positive photoresist.
Suitable materials for use as a filler include inorganic, organic,
organometallic, and polymeric materials, or their particulates. The
filler should be soluble or dispersible in the cleaning
solution.
Nonexclusive examples of filler materials may also include
water-dispersible or soluble polymers such as AQ.RTM. branched
polyesters (water-dispersible branched sulfopolyesters, Eastman
Chemical Company), CARBOSET.RTM. (carboxylated acrylic-based)
Polymers (BF Goodrich), polyvinylpyrrolidone, poly(vinyl alcohol),
poly(4-vinyl phenol), novolac resin, and their copolymers. More
preferable filler materials are non-film forming particles such as
latexes of PMMA, polystyrene, polyethylene and their carboxylated
copolymers and their corresponding salts, wax emulsions, colloidal
silica, titanium oxide, and calcium carbonate dispersions, and
mixtures thereof. Particularly preferable filler materials include
aqueous dispersions of ionomers of ethylene copolymers such as
ACQUA220.RTM. (zinc ionomer of ethylene copolymer),
ACQUA240.degree. (sodium ionomer dispersion of ethylene acrylic
acid copolymer), and ACQUA250.RTM. (N,N-diethylethanolamine)
(Honeywell, New Jersey). ACQUA220.RTM. and ACQUA250.RTM. can be
removed with conventional alkaline cleaners including the developer
used for typical novolac positive photoresists. ACQUA240.RTM. can
be removed with hot or cold water. The dispersability or solubility
of the fillers particularly the particulate fillers, may be
enhanced by the use of additives such as surfactants, dispersing
agents, KOH, triethanolamine, aromatic or aliphatic bases, aromatic
or aliphatic acids, pre-exposed positive novolac photoresists, and
water soluble polymers such as polyethylene glycol, polyvinyl
alcohol, polyvinylpyrrolidone, polyvinylpyridine, polyacrylic acid,
polymethacrylic acid, polyacrylamide, and their copolymers.
It has been found that the use of positive photoresist as a filler
is particularly useful in applications for the selective opening,
filling and sealing of relatively shallow microcups. If the
microcup is totally filled with unexposed positive photoresist, the
preferred microcup depth is less than 10 microns, and more
preferably, less than 5 microns. For deeper microcups, a positive
photoresist can be under-coated into the microcup, exposed and then
over-coated with a layer of positive photoresist.
In the second aspect of this invention, the microcups containing
the fillers are over-coated with a positive photoresist by using
Myrad bar, gravure, doctor blade, slot coating or slit coating, or
a similar device. A variety of commercially available positive
photoresists are suitable for this invention. Examples include
novolac based photoresists such as S-1818, SJR-1075, SJR-3000,
SJR-5440, SJR-5740, APEX.RTM.-E DUV (Shipley Company), AZ-9260,
AZ-4620, AZ-4562 (AZ Electronic Materials, Clariant AG), and
THB-Positive (JSR Microelectronics). In the case that the
positively working photoresist itself is also the filler,
photoresists used for thick coating applications such as SJR-5440,
SJR-5740 and those containing the t-BOC component are
preferred.
In over-coating of the microcups, an excess of photoresist is
usually applied in a sufficient amount to ensure that the microcups
are fully covered by the resist. Preferably, application of the
photoresist over the filled microcups is made such that the
thickness of the resist layer above the top surface of the
microcups is controlled to be in a range of about 0.1 to 5 microns,
more preferably from about 0.5 to 3 microns. Precision coating of
the resist may be performed using known procedures and devices such
as a Myrad bar, gravure, doctor blade, slot coating or slit
coating, or a related device. Excess photoresist over the microcups
may be removed using a number of methods known in the art,
including scraping with a wiper blade or similar device. The
photoresist is then baked in the oven by using standard procedures
as suggested by photoresist suppliers. Subsequent imagewise
exposure of the photoresist may be performed using a UV light
source such as Loctite Zeta 7410 exposure unit equipped with a
metal halide lamp with an intensity of about 6 mW/cm2 at 365 nm, or
ORIEL 87000 Series UV System equipped with 500 watts Model 68810
Mercury ARC Lamp with an intensity of about 5 mW/cm.sup.2 at 365
nm. Exposure is performed for a period of time sufficient to show
image discrimination with good contrast after the photoresist is
developed by a developer.
In the third aspect of the present invention, a synchronized
exposure mechanism is employed. In effect, a photomask loop is
"rolled" in a synchronized motion relative to a web, so as to
maintain alignment and registration between the mask and the web
during exposure. In a continuous synchronized motion and exposure
process, the web and mask are moved at the same speed in the same
direction during exposure in order to maintain this constant
alignment and registration. Imagewise exposure of the photoresist
on selected discrete microcups can be achieved precisely and
continuously on the web.
In the fourth aspect of the present invention, the exposed positive
photoresist on selected microcups is developed and removed using a
developer such as DEVELOPER 351.RTM. (sodium hydroxide, sodium
tetraborate decahydrate and borate solution) and DEVELOPER 453.RTM.
(potassium hydroxide and borate solution), both of Shipley Company,
Marlborough, Mass. The uncovered microcups may then be thoroughly
washed with distilled water or a diluted developer solution to
remove the filler material. Surfactants, such as TRITON.RTM. X-100
(polyethylene glycol tert-octylphenyl ether, Union Carbide),
AEROSOL.RTM. OT (wetting agents for use in reducing the interfacial
tension between liquids and solids or between two immiscible
liquids), sodium dodecylbenzene sulfonate may be added to improve
the efficiency of removal of the filler in the exposed areas. The
developed and cleaned microcups are then dried by using air flow,
heat, or vacuum, etc.
In the fifth aspect of the invention, the opened microcups are
filled with the first color display fluid, optionally containing a
thermoplastic or thermoset precursor (see below), using standard
coating methods as those used to coat the photoresist and filler
material onto the microcups. Alternatively, the filling may be
accomplished by methods such as screen printing, gravure printing,
inkjet printing or the like.
Various color display fluids and suspensions are known in the art,
including liquid crystals containing dichroic dyes of various
colors, and different color electrophoretic fluids as described in
co-pending '818 and '098 Patents.
In the sixth aspect of the invention, the filled microcups are
sealed. Sealing of the microcups can be accomplished by a variety
of methods described in the co-pending '818 and '098 Patents. In
one of the preferred embodiments, sealing may be accomplished by
dispersing a thermoplastic or thermoset precursor in the EPD fluid.
The compositions of the display fluid and the thermoplastic or
thermoset precursor are selected such that the display fluid is
immiscible with the precursor which has a specific gravity lower
than that of the display fluid. After filling the microcups with
the precursor/display fluid mixture, the precursor phase separates
from the color display fluid and forms a supernatant layer which is
then hardened or cured by solvent evaporation, interfacial
reaction, moisture, heat or radiation. Preferably, the sealing
layer is hardened by radiation, such as UV, although a combination
of two or more methods as described above may be used to increase
the throughput of the sealing step.
Alternatively, sealing of the microcups may be accomplished by
overcoating the display fluid with a solution of thermoplastic or
thermoset precursor. The sealing is accomplished by hardening the
precursor by solvent evaporation, interfacial reaction, moisture,
heat, radiation, or a combination of various curing mechanisms.
Preferably, the overcoating solution is lighter than the display
fluid and has a limited miscibility with the latter to reduce the
degree of intermixing during coating. Good coating uniformity and
satisfactory adhesion between the sealing layer and the microcup
array can be achieved by carefully adjusting surface tension and
viscosity of the overcoating solution.
The complete manufacturing steps as described above may be repeated
using other selected colored display fluids in the desired
configuration to fill in the selected microcups. The filled and
sealed multicolor microcup array is then laminated onto a conductor
film such as ITO on PET with an adhesive.
The EPDs manufactured according to the present invention may be
applied to the roll-to-roll continuous, or semi-continuous
manufacturing operation of thin, highly flexible, and durable
multi-color displays with excellent color addressability for many
different applications.
The EPD prepared according to the present invention is not
sensitive to manufacturing environment, such as humidity and
temperature. The resulting display is thin, flexible, durable,
easy-to-handle, and format-flexible. Since the EPD prepared
according to the present invention comprises microcups of favorable
aspect ratio and well-defined shape and size, the bi-stable
reflective display has excellent color addressability, high
contrast ratio, and fast switching rate.
Definitions:
"Aspect ratio" refers to the depth (or height) to width, depth to
length, or depth to diameter ratio of the microcups.
The term "well defined" herein is used to describe microcups or
cells, and indicates that the microcup or cell has a definite
shape, size and aspect ratio which are pre-determined according to
the specific parameters of the manufacturing process.
EXAMPLES
Example 1
Microcup Formulation
35 Parts by weight of Ebecryl 600 (UCB), 40 parts of SR-399
(Sartomer), 10 parts of Ebecryl 4827 (UCB), 7 parts of Ebecryl 1360
(UCB), 8 parts of HDDA (UCB), 0.05 parts of Irgacure 369 (Ciba
Specialty Chemicals), and 0.01 parts of isopropyl thioxanthone
(ITX, Aldrich) were mixed homogeneously and used for
micro-embossing.
Example 2
Preparation of Microcup Array
A primer solution comprising of 5 parts of Ebecryl 830, 2.6 parts
of SR-399 (Sartomer), 1.8 parts of Ebecry 1701, 1 part of PMMA
(Mw=350,000, Aldrich), 0.5 parts of Irgacure 500, and 40 parts of
methyl ethyl ketone (MEK) was coated onto a 2 mil 60 ohm/sq.
ITO/PET film (Sheldahl Inc., MN) using a #3 Myrad bar, dried, and
UV cured by using the Zeta 7410 (5 w/cm.sup.2, Loctite) exposure
unit for 15 minutes in air. The microcup formulation prepared in
Example 1 was coated onto the treated ITO/PET film with a targeted
thickness of about 50 .mu.m, embossed with a Ni--Co male mold
having a 60 (width) .mu.m.times.60 (length) .mu.m repetitive
protrusion pattern with 10 .mu.m wide partition lines and UV cured
from the PET side for 20 seconds, removed from the mold with a 2''
peeling bar at a speed of about 4-5 ft/min. Well-defined microcups
with depth ranging from 10 to 50 .mu.m were prepared by using male
molds having corresponding protrusion heights.
Example 3
Comparative Example
Microcup Array Laminated with Novolac Photoresist
3 Grams/M.sup.2 (dried) of the positively working photoresist
SJR-5740 (Shipley, Mass.) was coated on a removable clear support
PET-4851 (Saint-Gobain, Mass.) with a Myrad bar. Onto the
photoresist, 3 gm/m.sup.2 (dried) of an alkali-developable adhesive
composition comprising 9 parts of Nacor 72-8685 (50% solid,
National Starch) and 91 parts of 20% aqueous solution of Carboset
515 (BF Goodrich) was then coated with a Myrad bar. The three layer
adhesive/photoresist/support was then laminated at 40.degree. C.
onto a 10 micron deep and empty microcup array prepared according
to Example 2. The PET support was removed, and the photoresist
laminated microcup array was imagewise exposed through a photomask
using the Zeta 7410 (5 w/cm.sup.2, Loctite) exposure unit for about
1 minute and then developed by Developer-453 (Shipley) for 2
minutes. Deterioration of photoresist integrity in the non-exposed
regions such as pin holes and delamination of photoresist from the
microcups was observed after the development step.
Example 4
10 Micron Deep Microcups Fully Filled with Photoresist
A 10 micron deep microcup array prepared according to Example 2 was
corona treated with the BD-10A corona surface treater
(Electron-Technic Products, Inc, Chicago, Ill.) for about 1 minute,
then coated with photoresist SJR-5740 (42.5% solid) by using a #8
Myrad bar. The photoresist thickness above the top surface of the
microcups was measured to be about 3 microns. The coated microcup
array was imagewise UV exposed using the Zeta 7410 exposure unit
for about 1 minute and then developed by Developer-453 (Shipley)
for 2 minutes. Good image discrimination with no deterioration of
photoresist integrity on the partition wall in the non-exposed
regions was observed. The exposure-development cycle was repeated
once. No deterioration of photoresist integrity on the partition
wall in the non-exposed regions was observed after the second
development process.
Example 5
Comparative Example
40 Micron Deep Microcups Fully Filled with Photoresist
The same procedure was performed as in Example 4, except that a 40
micron deep microcup array was used and the exposure time and
development time were increased to 2 minutes and 13 minutes,
respectively. Some defects and undesirable development of the
photoresist on the partition wall in the non-exposed area were
observed after the second development process.
Example 6
Microcups Filled with Particulate Filler and Over-coated with
Photoresist
A 35 micron depth microcup array prepared according to Example 2
was used. A filler composition containing 1 part of 10% aqueous
solution of PVA 205 (Air Product) and 9 parts of a polystyrene
latex (50% solid) was coated onto the microcups using a Universal
Blade preset at a 25 micron gap opening. The microcup array was
dried and an optical microscope examination was performed to
confirm slightly under-filled microcups. The filled microcup array
was overcoated with the positive photoresist SJR-5740 by using a
Universal Blade preset at a 10 micron gap opening. The targeted
thickness of the photoresist above the filler was 3 microns. After
imagewise exposure for 30 seconds, the microcup array was developed
with Developer-453 for 1 minute followed by a thorough rinse with
de-ionized water. The exposure-development-washing cycle was
repeated once. No deterioration of photoresist integrity on the
partition wall in the non-exposed regions was observed after the
second cycle.
Example 7
Microcups Filled with Particulate Filler and Coated with
Photoresist
The same procedure was performed as in Example 6, except the
polystyrene latex was replaced by ACqua220, ACqua240, and ACqua250
(Honeywell, New Jersey) in three separate experiments. Excellent
image discrimination without defect in the non-exposed regions was
observed after the second cycle.
Example 8-13
Fillers Containing Photosensitive Solubility Inhibitor
The procedure was performed as in Example 6, except that the filler
was replaced by the composition shown in Table 1. Thus, 0-20% of a
photoactive compound, 4-t-butylphenol 215 ester (St-Jean
Photochemical) and 0-10% of polyvinylphenol (Aldrich, Mn=8000 or
Mn=20,000) were added to the water dispersible resin AQ-1350
(Eastman Chemical) in MEK and coated onto microcups. The slightly
under-filled microcups were blanket exposed for 2 minutes then
overcoated with the photoresist SJR-5740 by using a Universal Blade
preset at a 7 micron gap opening. The photoresist overcoated
microcup array was imagewise exposed for 30 seconds and developed
by the Developer-453 for 2 minutes. The exposure-development cycle
was repeated once. No deterioration of photoresist integrity on the
partition wall in the non-exposed regions was observed after the
second cycle.
TABLE-US-00001 TABLE 1 Fillers containing exposed photosensitive
solubility inhibitor (parts by weight) Example PVPL- PVPL- No.
AQ-1350 PAC 8,000 20,000 8 100 0 9 100 10 10 100 10 10 11 100 10 10
12 100 20 13 100 20 10 PAC = 4-t-Butylphenol 215-ester; PVPL =
Poly(4-vinyl phenol).
Example 14
Exposed Novolac Photoresist as the Filler
The same procedure was performed as in Examples 8-13, except the
filler was replaced by the photoresist SJR-5740. The
exposure-development cycle was repeated once. No deterioration of
photoresist integrity on the partition wall in the non-exposed
regions was observed after the second cycle.
Example 15
TiO.sub.2 Dispersion
6.42 Grams of Ti Pure R706 (Du Pont) were dispersed with a
homogenizer into a solution containing 1.94 grams of Fluorolink D
(Ausimont), 0.22 grams of Fluorolink 7004 (Ausimont), 0.37 grams of
a fluorinated copper phthalocyanine dye (3M), and 52.54 grams of
perfluoro solvent HT-200 (Ausimont).
Example 16
TiO.sub.2 Dispersion
The same procedure was performed as in Example 15, except that the
Ti Pure R706 and Fluorolink were replaced by a polymer coated
TiO.sub.2 particles PC-9003 (Elimentis, Highstown, N.J.) and Krytox
(Du Pont), respectively.
Example 17
Microcup Sealing
A microcup array of 35 microns depth prepared in Example 2 was
used. 85 Parts of the TiO.sub.2 dispersion prepared in Example 15
were diluted with 15 parts of a perfluoro solvent FC-77 (3M) and
coated onto microcups by using a Universal Blade Applicator with a
0.1 mil gap opening. A slightly underfilled microcup array was
obtained. A 7.5% solution of polyisoprene in heptane was then
over-coated onto the partially filled cups by a Universal Blade
Applicator with a 6 mil opening. The overcoated microcups were then
dried at room temperature. A seamless sealing layer of about 6
micron thickness was observed under microscope. No entrapped air
bubbles were observed in the sealed microcups.
Example 18
Microcup Sealing
The same procedure was performed as in Example 17, except the
TiO.sub.2 dispersion prepared in Example 16 was used. A seamless
sealing layer of about 6 micron thickness was observed under
microscope. No entrapped air bubbles were observed in the sealed
microcups.
While particular forms of the invention have been illustrated and
described, it will be apparent that various modifications can be
made without departing from the spirit and scope of the invention.
Accordingly, it is not intended that the invention be limited,
except as by the appended claims.
* * * * *